You're mistaken. There are many exceptions to the evidentiary rules against hearsay in the US, and one of the more common exceptions is a statement made by the opposing party (i.e. while the prosecution is questioning a witness, a statement made by the defendant to that witness) (Rule 801(d)(2)). It's evidence.
Your issues with the credibility of those witnesses are valid, and the defense had the opportunity to bring those issues up at trial (that's why we have jury trials and why you have a right to defend yourself at your jury trial). They certainly weren't the only pieces of evidence against him (there's a lot), and I'm sure the jury considered that.
You're mistaken. There are many exceptions to the evidentiary rules against hearsay in the US, and one of the more common exceptions is a statement made by the opposing party (i.e. while the prosecution is questioning a witness, a statement made by the defendant to that witness) (Rule 801(d)(2)). It's evidence.
Your issues with the credibility of those witnesses are valid, and the defense had the opportunity to bring those issues up at trial (that's why we have jury trials and why you have a right to defend yourself at your jury trial). They certainly weren't the only pieces of evidence against him (there's a lot), and I'm sure the jury considered that.